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From:   Mathieu Malaterre <malat@debian.org>
Date:   Mon, 18 Jun 2018 20:45:46 +0200
Message-ID: <CA+7wUszG3Tmq5qT7o7w7ttAU+bzyJfRORL_Qzk4wUG6y2gZUuw@mail.gmail.com>
Subject: Re: [PATCH] Revert "net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends"
To:     eric.dumazet@gmail.com
Cc:     schwab@linux-m68k.org, "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Christophe LEROY <christophe.leroy@c-s.fr>,
        Meelis Roos <mroos@linux.ee>, netdev@vger.kernel.org,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
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On Mon, Jun 18, 2018 at 8:18 PM Eric Dumazet <eric.dumazet@gmail.com> wrote:
>
>
>
> On 06/18/2018 10:54 AM, Andreas Schwab wrote:
> > On Jun 17 2018, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> >
> >> Oh this is silly, please try :
> >>
> >> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> >> index c642304f178ce0a4e1358d59e45032a39f76fb3f..54dd9c18ecad817812898d6f335e1794a07dabbe 100644
> >> --- a/net/core/skbuff.c
> >> +++ b/net/core/skbuff.c
> >> @@ -1845,10 +1845,9 @@ EXPORT_SYMBOL(___pskb_trim);
> >>  int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len)
> >>  {
> >>         if (skb->ip_summed == CHECKSUM_COMPLETE) {
> >> -               int delta = skb->len - len;
> >> +               __wsum csumdiff = skb_checksum(skb, len, skb->len - len, 0);
> >>
> >> -               skb->csum = csum_sub(skb->csum,
> >> -                                    skb_checksum(skb, len, delta, 0));
> >> +               skb->csum = csum_block_sub(skb->csum, csumdiff, len);
> >>         }
> >>         return __pskb_trim(skb, len);
> >>  }
> >
> > That doesn't help either.
> >
> > Andreas.
> >
>
> Then maybe NIC provided csum is not correct.
>
> It does not compute a checksum on all the frame, but part of it.
>
> You could use this patch to double check.
>
> diff --git a/drivers/net/ethernet/sun/sungem.c b/drivers/net/ethernet/sun/sungem.c
> index 7a16d40a72d13cf1d522e8a3a396c826fe76f9b9..277859ea73e35271a10b02011120fca248ec8e71 100644
> --- a/drivers/net/ethernet/sun/sungem.c
> +++ b/drivers/net/ethernet/sun/sungem.c
> @@ -857,6 +857,11 @@ static int gem_rx(struct gem *gp, int work_to_do)
>
>                 csum = (__force __sum16)htons((status & RXDCTRL_TCPCSUM) ^ 0xffff);
>                 skb->csum = csum_unfold(csum);
> +               {
> +               __wsum rsum = csum_partial(skb->data + ETH_HLEN, len - ETH_HLEN, 0);
> +               if (csum != csum_fold(rsum))
> +                       pr_err_ratelimited("sungem wrong csum : %x/%x, len %u bytes\n", csum, csum_fold(rsum), len);
> +               }
>                 skb->ip_summed = CHECKSUM_COMPLETE;
>                 skb->protocol = eth_type_trans(skb, gp->dev);
>
>

Here is what I get on my side

[   53.628847] sungem: sungem wrong csum : 4e04/f97, len 64 bytes
[   53.667063] sungem: sungem wrong csum : eea8/6eec, len 149 bytes
[   58.648952] sungem: sungem wrong csum : 2095/3d06, len 64 bytes
[   58.669414] sungem: sungem wrong csum : 5245/b50, len 149 bytes
[   63.674451] sungem: sungem wrong csum : 2d8/5abd, len 149 bytes
[   68.678233] sungem: sungem wrong csum : b8fc/a498, len 149 bytes
[   73.685771] sungem: sungem wrong csum : 374/5a21, len 149 bytes
[   78.689089] sungem: sungem wrong csum : d81/5014, len 149 bytes
[   83.683261] sungem: sungem wrong csum : 4e04/f97, len 64 bytes
[   83.690193] sungem: sungem wrong csum : c2f7/9a9d, len 149 bytes
[   88.692511] sungem: sungem wrong csum : f4d8/68bc, len 149 bytes
[   93.699915] sungem: sungem wrong csum : 1370/4a25, len 149 bytes
[   98.703136] sungem: sungem wrong csum : e1b5/7bdf, len 149 bytes
[  103.704230] sungem: sungem wrong csum : 5321/a74, len 149 bytes
[  108.688912] sungem: sungem wrong csum : 2095/3d06, len 64 bytes
[  108.706559] sungem: sungem wrong csum : ddbc/7fd8, len 149 bytes
[  113.713189] sungem: sungem wrong csum : 5a65/330, len 149 bytes
[  113.891697] sungem: sungem wrong csum : 4e04/f97, len 64 bytes
[  118.717151] sungem: sungem wrong csum : f7c8/65cc, len 149 bytes
[  123.722680] sungem: sungem wrong csum : 3d7a/201b, len 149 bytes
[  128.726524] sungem: sungem wrong csum : c8fd/9497, len 149 bytes
[  133.732045] sungem: sungem wrong csum : de0d/7f87, len 149 bytes
[  135.529163] sungem: sungem wrong csum : 3089/b6dd, len 96 bytes
[  135.529208] eth0: hw csum failure
[  135.529220] CPU: 0 PID: 0 Comm: swapper Not tainted 4.17.0+ #7
[  135.529226] Call Trace:
[  135.529243] [dffedbe0] [c069ddac]
__skb_checksum_complete+0xf0/0x108 (unreliable)


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